The X-linked gene Pem is a member of the homeobox transcription factor family expressed in a developmentally regulated manner in specific somatic cell types in both the male and female reproductive tracts. In male mice and rats, Pem is expressed exclusively in Sertoli cells in the testis and in principal cells in the caput region of the epididymis. Pem is necessary for optimal fertility, as a null mutation in Peru decreases the number of spermatids in the testis, decreases caudal sperm counts, increases the frequency of immotile caudal sperm, and causes subfertility. Thus, Pem-null mice may be a model system for elucidating mechanisms that cause male subfertility, a relatively common condition in humans. Microarray and real-time PCR analyses revealed the existence of several genes exhibiting altered expression in Pem-null mice testes. Some of these encode secreted proteins involved in energy metabolism, including insulin II, resistin, and adiponectin. Other unique properties of Pem make it a useful for determining how genes are regulated in somatic cells of the male reproductive tract. Transgenic mice studies revealed that a 0.3-kb region (region I) immediately upstream of the Peru proximal promoter (Pem Pp) drives Sertoli cell-specific expression in the testis, expression in the epididymis, and androgen-dependent expression in both of these organs. Another short region (region II) controls stage-specific Sertoli cell expression (both in neonates and adults) and directs region-specific expression in the epididymis. Although other gene promoters expressed in Sertoli and epididymal cells have been defined, no other short sequences that specify expression in only those cells have been identified, and little is known about the molecular regulation of these other gene promoters in vivo. The Pem regulatory elements may be useful for selectively ablating and expressing genes specifically in Sertoli and epididymal cells in vitro and in vivo. The first Aim is to determine how Pem causes male subfertility and to elucidate the transcriptional networks under its control in somatic cells of the male reproductive tract. The second Aim is to use the Pem Pp as an in vivo model system to identify and characterize regulatory elements and transcription factors that direct Sertoli cell-specific expression in the testis, developmentally regulated expression in Sertoli cells, region-specific expression in the epididymis, and androgen-dependent expression in both Sertoli and epididymal cells. [unreadable] [unreadable]